Epitaxial growth and structure of highly mismatched oxides with rock-salt structure on MgO

Abstract

Thin films of oxides with rock-salt structure were grown on (0 0 1)MgO single crystal substrates to study the influence of a high lattice mismatch ε s on growth phenomena via the chemical solution deposition method using toluene solutions of different 2-ethylhexanoates and neodecanoates. The films were pyrolyzed to crystallize the desired oxide and heat treated up to 1400°C to promote epitaxial growth. X-ray texture analyses, SEM and TEM investigations of CaO on MgO ( ε s≈14.2%) showed that the films broke into single crystal islands. The preferred epitaxial orientation relationships are [ 1 ̄ 1 0] (1 1 1)CaO∥〈1 1 0〉(0 0 1)MgO (four variants for reasons of symmetry). A two-dimensional near-coincidence site lattice (NCSL) model ( Σ * CaO=7/ Σ * MgO=8) is presented for the interface. For the higher mismatched system SrO on MgO ( ε s≈22.5%), SEM investigations and X-ray ( θ−2 θ) measurements suggest that the growth orientation has changed to (0 0 1)SrO∥(0 0 1)MgO with a few discrete in-plane rotations. The measured orientations correlate well with a two-dimensional NCSL model of rotated cubic SrO crystallites. The mechanisms leading to the experimentally observed structures and morphologies are discussed with respect to the influence of lattice mismatch.